JP3593058B2 - Optical amplifier - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplifying device that compensates for a predetermined gain profile required in an optical transmission system even when some of a plurality of laser units constituting a pump light source fail.
[0002]
[Prior art]
Due to the rapid spread of the Internet in recent years and the rapid increase of intra-company LAN connections, not only the number of communication calls but also the content data to be transmitted tends to increase in capacity like moving images. The proliferation of data traffic is a problem. Therefore, in order to prevent a decrease in communication performance due to an increase in data traffic, WDM (Wavelength Division Multiplexing) systems have been remarkably developed and spread.
[0003]
In the WDM system, large-capacity transmission that is 100 times as large as that of the conventional one is realized by one fiber by putting a plurality of optical signals on different wavelengths. In particular, the existing WDM system enables wideband and long-distance transmission by using an erbium-doped fiber amplifier (hereinafter, EDFA). Here, when the EDFA passes through a special optical fiber doped with an element called erbium with a pumping laser having a wavelength of 1480 nm or 980 nm, light having a wavelength of 1550 nm as a transmission signal is amplified in the special fiber. This is an optical amplifying device that applies the principle of being performed.
[0004]
On the other hand, an EDFA is a centralized optical amplifier in which a portion that excites an optical signal is concentrated, and the EDFA reduces transmission line optical fiber loss leading to accumulation of noise and nonlinearity that causes signal distortion and noise. There was a limit to receive. Furthermore, the EDFA enables optical amplification in a wavelength band determined by the band gap energy of erbium, and it has been difficult to widen the band to realize further multiplexing.
[0005]
Therefore, a Raman amplifier has attracted attention as an optical amplifying device replacing the EDFA. The Raman amplifier is a distributed optical amplifier that does not require special fibers such as erbium-doped fiber like EDFAs and uses a normal transmission line fiber as a gain medium, so it can be used in conventional WDM transmission systems based on EDFAs. It has a feature that the transmission quality can be improved as compared with the prior art.
[0006]
FIG. 5 is a block diagram showing a schematic configuration of a conventional Raman amplifier. In FIG. 5, the Raman amplifier includes an optical multiplexer 120 provided on the transmission line 99, optical isolators 111 to 113, and a high-power pumping unit (HPU: High-power Pumping Unit) 130.
[0007]
FIG. 6 is a diagram illustrating a configuration example of the HPU 130. In FIG. 6, the HPU 130 includes six laser units LD1 to LD6 having different oscillation center wavelengths and a Mach-Zehnder WDM coupler 131. Further, each of the laser units LD1 to LD6 includes two Fabry-Perot type semiconductor lasers 134 having the same oscillation center wavelength. The laser output of each of the semiconductor lasers 134 is wavelength-stabilized by a fiber Bragg grating 133 (FBG), and polarization is also increased. The signals are combined by a combiner (PBC) 132 to form one output. The polarization combining by the PBC 132 is a measure for increasing the pumping power of each oscillation center wavelength and reducing the polarization dependency of the Raman gain. As described above, since the HPU 130 needs to amplify signal light of a plurality of multiplexed wavelengths (channels), the HPU 130 includes a plurality of laser units having different oscillation center wavelengths.
[0008]
The laser outputs output from the laser units LD1 to LD6 are further multiplexed by the WDM coupler 131 and output as high-power multiplexed pump light. The pump light output from the HPU 130 passes through the optical fiber as the transmission line 99 via the optical multiplexer 120. FIG. 5 shows an example of backward pumping, and the pumping light multiplexed by the optical multiplexer 120 passes through the transmission path 99 in the opposite direction to the signal light.
[0009]
When the high-power pumping light passes through the transmission line 99, Raman scattered light shifted to a longer wavelength side by 110 nm than the pumping light is generated based on the material characteristics of the optical fiber as the transmission medium, and stimulated. After the Raman scattering process, the energy of the excitation light changes to signal light. Thereby, the signal light is amplified.
[0010]
As described above, the Raman amplifier is an amplifier that can amplify the signal light as it is by using the already laid optical fiber as an amplification medium. The EDFA is different from the EDFA in terms of the amplification medium, the number of excitation light sources used, the excitation power, and the like. The light source for exciting the erbium-doped fiber in the EDFA may have the same configuration as the HPU 130 described above.
[0011]
[Problems to be solved by the invention]
However, in an optical amplifying device such as an EDFA or a Raman amplifier, if even one of the laser units in the HPU 130 fails, the gain profile changes, and as a result, signal transmission without desired amplification is performed. There is a problem that the quality is deteriorated.
[0012]
FIG. 7 is a diagram showing an example of a gain profile for explaining this problem. In the HPU 130 shown in FIG. 6, assuming that the oscillation center wavelengths of the laser units LD1 to LD6 are 1435 nm, 1442.5 nm, 1450 nm, 1455 nm, 1465 nm, and 1480 nm, respectively, as shown by a dotted line 150 in FIG. It shows an almost flat gain profile from 1540 nm to 1600 nm.
[0013]
However, when the shortest wavelength side laser unit LD1 and the longest wavelength side laser unit LD6 are both unable to obtain an oscillation output of a predetermined value or more due to their life or failure, the above gain profile is shown in FIG. As shown by the solid line 160, the wavelengths are greatly distorted on the short wavelength side and the long wavelength side, and the effective amplification band is narrowed. That is, the signal power on the short wavelength side and the long wavelength side is reduced.
[0014]
The present invention has been made in view of the above, and even when some of a plurality of laser units constituting an excitation light source are out of order, it is possible to maintain optical transmission without deteriorating signal transmission quality. It is an object of the present invention to provide a light amplifying device that can be used.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a plurality of laser light sources that output laser lights having different oscillation center wavelengths and a monitor unit that detects output power of each laser light source, Among the plurality of laser light sources, laser light output from laser light sources other than the first laser light source having the shortest oscillation center wavelength and the second laser light source having the longest oscillation wavelength are multiplexed, and the multiplexed light is transmitted. A pump light source that outputs as a pump light to be amplified with a desired amplification band and a desired gain that are required for signal light propagating on the road, and output powers of the plurality of laser light sources according to an input control signal. A laser light source whose output is to be stopped from among the plurality of laser light sources, based on the control means for controlling the laser power and the output power detected by the monitor unit. Determining a gain profile when the light source is in a stopped state from a plurality of gain profiles stored in advance, and outputting output power information of each laser light source indicated by the selected gain profile as the control signal, Wherein, when the gain profile includes output power information for outputting a laser beam from at least one of the first laser light source and the second laser light source, the excitation light source includes the first laser light source. And a laser beam output from at least one of the second laser light sources is further combined and output.
[0016]
According to the present invention, the pump light source prepares a spare laser light source on the shorter wavelength side and the longer wavelength side than the number required for the minimum source to obtain the desired gain profile, so that the shortest wavelength side and the longest wavelength Even if the laser light source on the side stops due to a failure or the like, the desired gain profile can be secured.
[0017]
The invention according to claim 2 is characterized in that Raman amplification is performed on the signal light propagating on the transmission line by the pump light.
[0018]
According to the present invention, the protection operation of the excitation light source can be applied to the excitation light source used when performing Raman amplification.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of an optical amplifying device according to the present invention will be described in detail with reference to the drawings. In particular, here, an example is given of an optical amplifying device that performs Raman amplification. It should be noted that the present invention is not limited by the embodiment.
[0024]
FIG. 1 is a block diagram illustrating a schematic configuration of the optical amplifying device according to the embodiment. In FIG. 1, portions common to FIG. 5 are denoted by the same reference numerals, and description thereof is omitted. FIG. 1 is different from FIG. 5 in that an HPU 30 to which a laser unit for protection described later is added is provided instead of the conventional HPU 130, and a gain control unit 40, a determination unit 50, and a gain profile storage unit 60 are further provided. .
[0025]
The gain control unit 40 is a unit that controls the gain of each laser unit of the HPU 30 according to an instruction from the determination unit 50. The determining unit 50 monitors the failure of each laser unit of the HPU 30 and, when a failure occurs, instructs the gain control unit 40 to perform gain control based on the gain profile stored in the gain profile storage unit 60. It is. Here, the gain profile indicates a desired output power to be output to each laser unit of the HPU 30.
[0026]
FIG. 2 is a diagram illustrating a configuration example of the HPU 30. 2, the HPU 30 includes two laser units LD7 and LD8 in addition to the six laser units LD1 to LD6 shown in FIG. 6 (hereinafter, these laser units LD7 and LD8 are particularly referred to as protection laser units). And a Mach-Zehnder WDM coupler 31 for multiplexing lasers oscillated by the laser units LD1 to LD8.
[0027]
As shown in FIG. 6, each of the laser units LD1 to LD8 includes two Fabry-Perot semiconductor lasers having the same oscillation center wavelength, and the laser output of each semiconductor laser is converted into a wavelength by a fiber Bragg grating (FBG). In addition to stabilization, the signals are multiplexed by a polarization combiner (PBC) and output as one signal.
[0028]
Here, in particular, the newly added laser unit LD7 oscillates at an oscillation center wavelength shorter than the shortest wavelength among the oscillation center wavelengths of the laser units LD1 to LD6. Conversely, the laser unit LD8 oscillates at an oscillation center wavelength longer than the longest wavelength among the oscillation center wavelengths of the laser units LD1 to LD6. Referring to the example used in the description of FIG. 6, the oscillation center wavelengths of the laser units LD1 to LD6 are 1435 nm, 1442.5 nm, 1450 nm, 1455 nm, 1465 nm, and 1480 nm, respectively. The wavelength is 1427.5 nm, and the oscillation center wavelength of the laser unit LD8 is 1495 nm.
[0029]
That is, the HPU 30 can provide a gain profile with a wider amplification band by adding the laser units LD7 and LD8, as compared with the case where only the laser units LD1 to LD6 are used.
[0030]
In FIG. 2, optical demultiplexers C1 to C8 are provided on output transmission paths of the laser units LD1 to LD8, respectively, and the optical demultiplexers C1 to C8 are respectively monitored by the demultiplexers. The sections M1 to M8 are connected. That is, the laser beams output from the laser units LD1 to LD8 are input to the monitor units M1 to M8 via the optical demultiplexers C1 to C8. The monitoring units M1 to M8 are means for receiving the signal light demultiplexed by the optical demultiplexers C1 to C8 and detecting the signal light power, and are constituted by light receiving elements such as photodiodes.
[0031]
The determination unit 50 receives the signal light power values detected by the monitor units M1 to M8, and compares the signal light power value with a predetermined value to enable detection of a failure.
[0032]
Hereinafter, the operation of the optical amplifier according to the embodiment will be described. FIG. 3 is a diagram illustrating an example of a gain profile given to the gain control unit 40. First, it is assumed that all of the laser units LD1 to LD8 in the HPU 30 operate normally and output laser light with an output power according to the gain profile shown in FIG. As shown in FIG. 3A, especially when none of the laser units LD1 to LD6 has a failure, the laser units LD7 and LD8 for protection are turned off without performing laser oscillation.
[0033]
That is, this state is equivalent to the HPU 130 shown in FIG. 6, and the multiplexed light output from the WDM coupler 31 also shows a flat gain profile in a desired amplification band as shown by a dotted line 150 in FIG.
[0034]
In the above state, the determination unit 50 compares each signal light power value output from the monitor units M1 to M6 with a predetermined value, and determines whether the signal light power value has reached the predetermined value. As a result of the determination, when there is a laser unit that outputs a signal light that does not reach the predetermined value (or that does not output any signal light), the determination unit 50 determines that the operation of the laser unit is stopped. The gain profile to be adopted is extracted from the gain profile storage unit 60.
[0035]
For example, when the determination unit 50 determines that the signal light power of the laser units LD1 and LD6 has not reached the predetermined value due to a failure or the like, the laser units LD1 and LD6 are turned off as shown in FIG. At the same time, a gain profile in which an appropriate output power is set for the protection laser units LD7 and LD8, which have been in the OFF state, is extracted from the gain profile storage unit 60.
[0036]
Here, the gain profile stored in the gain profile storage unit 60 is at least a gain profile obtained when the laser units LD1 to LD6 are operated and the protection laser units LD7 and LD8 are turned off, that is, FIG. It is necessary to cover the amplification band which becomes effective by the gain profile shown in FIG. 7A and the dotted line 150 in FIG. For example, the gain profile shown in FIG. 3B shows a flat gain in the amplification band as shown by a solid line 170 in FIG.
[0037]
In particular, in the optical amplifying device according to the present embodiment, the oscillation center wavelength of the laser unit LD7 for protection is shorter than the shortest oscillation center wavelength of the laser unit for non-protection use, and the oscillation center wavelength of the laser unit LD8 for protection. Is set to be longer than the longest oscillation center wavelength of the laser unit other than the purpose of protection, as shown in FIG. 3 (b), the laser unit which outputs the laser having the shortest and longest oscillation center wavelengths at the time of failure has failed. Also in this case, by operating the laser units LD7 and LD8 for protection, the initial amplification band can be secured.
[0038]
As described above, according to the optical amplifying device according to the embodiment, it is necessary to stop the operation of the laser unit because one of the laser units constituting the HPU 30 has a failure or a decrease in output. If there is, the resulting distortion of the gain profile, together with the adjustment of the gain control of the other laser units, if necessary, activates the protection laser unit that will have the shortest wavelength and the longest wavelength oscillation center wavelength. Therefore, amplification with a desired flat gain profile can be ensured for the amplification band obtained before the failure.
[0039]
In addition, since the above protection operation is automatically performed inside the optical amplifier, it is necessary to go to the installation location of the optical amplifier to perform adjustment or replacement of the laser unit in order to secure a desired gain profile after a failure. And maintenance and management of the entire optical transmission system constructed using the optical amplifier can be facilitated.
[0040]
In the above-described embodiment, a configuration in which Raman amplification is performed as an optical amplifying device has been described as an example. However, in an EDFA, the pumping light source of the EDFA is replaced with the HPU 30, and the gain control unit 40, By providing the determination unit 50 and the gain profile storage unit 60, the same effect as described above can be obtained.
[0041]
【The invention's effect】
As described above, according to the optical amplifying device according to the present invention, the laser light source that generates the pump light has a shorter wavelength side and a longer wavelength side than the number of laser light sources that can secure a desired gain in a desired amplification band. The wavelength profile is increased on each side, and the distortion of the gain profile caused when one of the laser light sources is stopped due to a failure etc. is adjusted as necessary together with the adjustment of the gain control of the other laser light sources. Therefore, since the laser light source for protection having the shortest wavelength and the longest wavelength oscillation center wavelength is operated, it is necessary to secure amplification with a desired flat gain profile in the amplification band obtained before the failure. This has the effect that it can be performed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an optical amplifier according to an embodiment.
FIG. 2 is a diagram illustrating a configuration example of an HPU of the optical amplifier according to the embodiment;
FIG. 3 is a diagram illustrating an example of a gain profile given to a gain control unit of the optical amplifier according to the embodiment;
FIG. 4 is a diagram illustrating an example of a gain profile stored in the optical amplifier according to the embodiment;
FIG. 5 is a block diagram illustrating a schematic configuration of a conventional Raman amplifier.
FIG. 6 is a diagram illustrating a configuration example of a conventional HPU.
FIG. 7 is an explanatory diagram for explaining a problem in a conventional optical amplifier.
[Explanation of symbols]
30 HPU
31, 131 WDM coupler 40 Gain control unit 50 Judgment unit 60 Gain profile storage unit 99 Transmission lines 111 to 113 Optical isolator 120 Optical multiplexer 133 Fiber Bragg grating 134 Semiconductor lasers C1 to C8 Optical demultiplexers M1 to M8 Monitor units LD1 to LD1 LD6 Laser unit LD7, LD8 Laser unit for protection

Claims (2)

A plurality of laser light sources that output laser beams having different oscillation center wavelengths from each other and a monitor unit that detects the output power of each laser light source are provided, and the first oscillation center wavelength of the plurality of laser light sources is the shortest. A laser light output from a laser light source excluding the laser light source and the longest second laser light source is multiplexed, and the multiplexed light is converted into a desired light required as a minimum with respect to a signal light propagating on a transmission path. An excitation light source that outputs as amplification light to be amplified with an amplification band and a desired gain,
Control means for controlling the output power of the plurality of laser light sources according to the input control signal,
Based on the output power detected by the monitor unit, the laser light source to stop the output from the plurality of laser light sources is specified, and the gain profile when the specified laser light source is in the stop state is stored in advance. A determination means for selecting from a plurality of gain profiles and outputting output power information of each laser light source indicated by the selected gain profile as the control signal,
With
When the gain profile includes output power information for outputting laser light from at least one of the first laser light source and the second laser light source, the excitation light source includes the first laser light source and the second laser light source. An optical amplifying device, which further combines and outputs laser light output from at least one of the second laser light sources. The optical amplifier according to claim 1, wherein Raman amplification is performed on the signal light propagating on the transmission path by the pump light.

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